WX. Brown, Jr.
Reprinted from ENTOMOLOGICAL NEWS, Vol. LXIII, No. 3, March, 1952
Printed in U, S. A.
Notes on Leptothorax bradleyi Wheeler and
L. wheeled M. R. Smith (Hymenoptera :
By E. O. WILSON, Department of Zoology and Entomology,
University of Tennessee
Distributional data published up to the present for the closely
related species Leptothorax bradleyi and-L. wheeleri have out-
lined ranges which appeared to be mutually exclusive. When
I recently examined specimens of this complex from two local-
ities in Alabama, I considered that they might approach inter-
grades between the two species, thus indicating that the two
were actually subspecies. However, when representative spec-
imens were borrowed from most of the collections which have
been made of these forms, it was quickly established that the
Alabama material was typical bradleyi. Furthermore, the ranges
of the two species were found to overlap through at least three
states, definitely establishing them as distinct species. The
following paper consists of the new distributional data and
additional significant descriptions.
Workers of the two species are most easily distinguished on
the basis of sculpturing, but they also differ in alitrunk profile,
in proportions of the propodeal spines, and in size. In the
descriptions given below only the characters useful in com-
parison are emphasized.
p-^Jto c-t . ,
Leptothorax wheeleri M. R. Smith - S*~^~~*&+L> -.->.
L. wheeleri M. R. Smith, Ann. Ent. Soc. Amer., Vol. 22, p.
547, fig. 1 (1929). Workers and queens.
Worker. Ten workers representing all available records
showed the following measurements : alitrunk length 0.90 mm.-
1.13 mm., mean 1.04 mm.; head length 0.83 mm.-1.02 mm.,
mean 0.91 mm. ; distance between the tips of the propodeal
1 Appreciation is expressed to Dr. M. R. Smith, Dr. Arnold Van Pelt,
Dr. A. C. Cole, and Mr. H. T. Vanderford for the loan of most of
the material used in this study.
68 ENTOMOLOGICAL NEWS [Mar., 1952
spines 0.28 mm.-0.37 mm., mean 0.30 mm. ; le^th of propodeal
spines 0.17 mm.-0.22 mm., mean 0.18 mm. (^Sft measurements
with maximum error of 0.01 mm.) Alitrunks were measured
in profile from the dorsal base of the pronotal collar to the
dorsum of the junction with the petiole; heads were measured
in profile from the anterior edge of the clypeus to the extreme
Dorsum of head covered by longitudinal rugae, the interspaces
coarsely punctate.; the rugae extend forward past the fronto-
clypeal suture as the clypeal carinae. Alitrunk coarsely rugo-
reticulate. Petiole with distinct rugulae, fainter than those
of the alitrunk. Postpetiole with a few faint rugulae, the
interspaces punctate, the surface opaque.
Alitrunk arcuate in profile, rising to its highest point at the
Localities. Specimens were examined from the following
localities : Mississippi State College (M. R. Smith) ; Starkville,
Miss. (M. R. Smith) ; War Trace, Tenn. (H. T. Vanderford) ;
Greenbriar Cove, Great Smoky Mts. Nat. Park, Tenn. (A. C.
Cole) ; Wilmington, N. C. (H. T. Vanderford) ; Dalton, Ga.
(H. T. Vanderford) ; Gainesville, Fla. (T. H. Hubbell). Smith
also recorded this species from Adaton, Miss., and L. G. and
R. G. Wesson recorded it from South Central Ohio (Amer.
Mid. Nat, Vol. 24, p. 96).
Leptothorax bradleyi Wheeler
L. bradleyi Wheeler, Psyche, Vol. 20, p. 113 (1913). Holotype
Worker. Ten workers representing all of the available
records showed the following measurements : alitrunk length
0.83 mm.-0.93 mm., mean 0.89 mm.; head length 0.70 mm.-
0.80 mm., mean 0.74 mm. ; distance between the tips of the
propodeal spines 0.25 mm.-0.28 mm., mean 0.27 mm. ; length
of the propodeal spines 0.08 mm.-0.15 mm., mean 0.13 mm.
Alitrunk evenly flattened in profile.
Sculpturing of the head similar to that in L. wheeleri. The
entire mesonotum except for the margins finely rugulo-reticulate,
giving a granulose appearance at magnifications of 36 X and less.
Ixiii] . ENTOMOLOGICAL NEWS 69
The posterior edge of the pronotum similar to mesonotum, but
the anterior half rugo-reticulate. This reticulum merges with
the posterior rugulo-reticulum, and the latter decreases in size
anteriad until its interspaces are distinguished only as broad
punctures within the coarser, anterior reticulum. The margins
of the mesonotum longitudinally rugose. The reticulum of the
basal face of the propodeum fades posteriad into coarse punctula-
tion. The petiole punctate, opaque; sculpturing of the post-
petiole irregular, with very shallow punctures, feebly shining to
The colorations of L. bradleyi and L. wheeleri are nearly
identical, a rich ferruginous red. In most of the bradleyi work-
ers examined the posterior margins of the gastric segments are
distinctly infuscate; this condition is absent in wheeleri.
Queen. Alitrunk length 1.33 mm.; head length 0.86 mm.
Differing from the worker in the usual characters separating
these two castes, in sculpturing, and in proportions of the
propodeal spines. Mesonotal scutum and scutellum evenly
flattened in profile, the posterior third of the scutellum sloping
downward somewhat. The propodeal spines blunt and denti-
form. Notaulices and parapsidal furrows absent.
Head covered by relatively coarse, longitudinal rugae (ap-
proximately thirty would be cut by a line drawn transversely
across the center of the head) ; rugae variable in size, fre-
quently anastomosing; the interspaces punctate. Central por-
tion and collar of pronotum granulose, the pleural arms rugo-
reticulate, with the two zones of sculpturing meeting abruptly.
Mesothoracic scutum and epipleurites with finer, more evenly
longitudinal rugae (approximately forty would be cut by a line
drawn transversely across the center of the scutum) . Scutellum
with smaller, less regular, and indistinct rugae. Anterior margin
of the propodeum rugose, the remainder granulose. Sides of
the alitrunk mostly granulose, with a few marginal rugae.
Petiole and postpetiole with numerous shallow, confluent punc-
tures and a few indistinct longitudinal rugae ; their surfaces feebly
shining. The gaster without sculpturing, glabrous.
This queen differs very little from the cotype queen of L.
70 ENTOMOLOGICAL NEWS [Mar., 1952
wheeleri loaned to me by Dr. Smith. It can be distinguished
from Smith's specimen on the basis of the following characters :
distinct transverse rugae present between the propodeal spines
in wheeleri, absent in bradleyi; petiole and postpetiole opaque
in wheeleri, feebly shining in bradleyi; propodeal spines fairly
well developed in wheeleri, dentiform in bradleyi; and smaller
size of bradleyi. Otherwise the two closely resemble one an-
other in sculpturing, flattening of the alitrunk, infuscation of the
posterior margins of the gastric segments (absent in wheeleri
workers), and general habitus under low magnification. This
convergence of characters seems to indicate that the queen caste
has diverged more slowly than the worker caste. If this is true,
it appears that the bradleyi worker more closely approaches the
ancestral form, in weaker sculpturing, flattening of the alitrunk,
Male. Alitrunk length 1.23 mm.; head length 0.52 mm.
Antennae 12- jointed, with the funicular segments gradually
diminishing in size distally and not forming a distinct club.
Notaulices (Mayrian Furrows) present and distinct, converg-
ing directly behind the center of the mesonotum. Wings with
greatly reduced venation, the following veins occurring in the
forewing: Sc + R, R 1( Rsf 1; Rs + M, Rsf 5 , Mf 1; M +CuA, A,
cu-a. Mf 5 , CuA, and A distad to cu-a present but faded and
indistinct. In one of the two specimens examined a small cross-
vein (2r?) extends from Rsf 5 almost to the stigma. (See
BROWN and NUTTING, Trans. Amer. Ent. Soc., Vol. 75, pp.
113-132, for a discussion of homology.) Hindwing with two
very faint, basal abscissae. Costal, median, submedian, and
cubital cells present in the fore wing; discoidal cell absent.
Most of head covered by longitudinal rugulae, the interspaces
punctate, a condition approaching that of the worker ; rugae of
occiput indistinct, with a transverse trend. Most of the alitrunk
covered by longitudinal rugulae, but these are finer and more
closely set than those of head ; interspace punctulations not ap-
parent. Propodeum covered by shallow, confluent punctures.
Petiole, postpetiole, and gaster shining, largely free from sculp-
turing. All of body except appendages jet black. Scape and
Ixiii] ENTOMOLOGICAL NEWS 71
femora dark brown; funiculus and distal portion of legs light
brown. Wings faintly iridescent.
Localities. Specimens were examined from the following
localities : Bay Minette, Ala. (E. O. Wilson) ; Tuscaloosa, Ala.
(E. O. Wilson and Ben Sanders, Jr.) ; Hoschton, Ga. (H. T.
Vanderford) ; Gainesville, Fla. (A. Van Pelt) ; Lake Placid,
Fla. (T. C. Schneirla). The type locality is Billy's Island,
Okefenokee Swamp, Ga.
Knowledge of the biology of the two species is limited at
present to scanty nesting data. Smith found, the several
colonies comprising the type series of L. wheeleri in crevices
and cavities of solid deciduous trees and under the bark of
rotten pine stumps. Hubbs found his Florida wheeleri in gal-
leries in a stick of solid pine firewood. The .Wessons (Amer.
Mid. Nat., Vol. 24, p. 96) found this species "in galleries in the
hardened, weathered logs on old deserted and tumbledown log
cabins exposed to the sun. Two other colonies were found
on large oak trees where they were nesting in dead stobs."
Most of the other specimens of both species have been collected
as strays. My two colonies of L. bradleyi were found by chip-
ping away the thick bark of living pines. Both were in flat, well
defined galleries in the bark about three to five feet above the
ground. The Tuscaloosa nest was carefully dissected, and what
probably represents the bulk of the colony was collected; this
contained one dealate queen, 42 workers, two males, and a
small number of worker larvae and pupae.